In present day molten iron production lines, the blast furnace iron making process represents the predominant method. Recently, the smelting reduction ironmaking process with shaft type reduction furnace using the pellets and lump ores has been commercialized to produce molten iron. However, the above two processes have the restriction that only agglomerated raw materials can be used.
In the blast furnace ironmaking process, a sintered ore is employed which is made by mixing coke (made from coal), plus fine iron ores and flux, thereby producing a molten iron. In this method, facilities for the pre-treatment of the raw material are required, and in this connection, the environmental pollution problem has become serious. Thus, regarding this matter, environmental regulation has been imposed.
Meanwhile, in the shaft type smelting reduction ironmaking process, pellets and/or lump ores are used to produce molten iron. Thus in the blast furnace ironmaking process or in the shaft type smelting reduction ironmaking process, fine iron ores cannot be directly used, but a pre-treatment has to be carried out. Therefore, the fluidized bed type smelting reduction ironmaking process has gained attention as a means to replace the existing blast furnace ironmaking process, because the fluidized bed type smelting reduction ironmaking process can directly use fine iron ores which are cheap and abundant. Furthermore, it can lower the investment costs and environmental pollution by removing the raw material pre-treatment facilities. Therefore, studies on the fluidized bed type smelting reduction ironmaking process are being briskly pursued.
The smelting reduction ironmaking process is divided into a pre-reduction stage and a final reduction stage. At the pre-reduction stage, the raw ores are pre-reduced into a solid state, while at the final reduction stage, the pre-reduced iron is put into a melting furnace to produce a finally reduced pig iron. Generally, the pre-reduction stage is classified into a moving bed type and a fluidized bed type. It is known that the fluidized bed type is advantageous in the case of a fine iron ore, because the fluidized bed type smelting reduction ironmaking process pre-reduces the raw iron ore by means of the reducing gas within the reduction furnace. That is, the fluidized bed type smelting reduction ironmaking process is efficient in permeability and gas utilization.
FIG. 1 illustrates a conventional fluidized bed type pre-reduction apparatus, which is disclosed in Korean Patent No. 81002.
As shown in FIG. 1, the conventional fluidized bed type pre-reduction apparatus includes: a first pre-reduction furnace 10 disposed above, twin type second and third pre-reduction furnaces 20 and 30 disposed below, cyclones 40, 50 and 60, and circulation pipes 15, 24, 41, 51 and 61. In the first pre-reduction furnace 10, a raw fine iron ore which has been charged through a charging hopper 70 forms a bubbling fluidization by the help of an off-gas of the third cyclone 60. Then the fine iron ore undergoes drying and pre-heating steps to be supplied through the second circulation pipe 15 to the second pre-reduction furnace 20. Within the second pre-reduction furnace 20, the intermediate and fine iron ore particles among the first pre-reduced iron ore of the first pre-reduction furnace fly to the third pre-reduction furnace 30, while only the coarse iron ore particles form bubbling/turbulent fluidization to be pre-reduced for the second time. In the third pre-reduction furnace 30, the first pre-reduced intermediate/fine iron ores which have been flown from the second pre-reduction furnace 20 through the fourth circulation pipe 24 form a high speed fluidization to be reduced for the second time. The fine iron ore particles which have been flown from the first pre-reduction furnace are collected by the first cyclone 40 to be circulated through the first circulation pipe 41 into the second pre-reduction furnace. The fine iron ore particles which have been flown from the third pre-reduction furnace are collected by the second cyclone 50 to be circulated through the fifth circulation pipe 51 partly to the third pre-reduction furnace and partly to be discharged to a fifth outlet 52. The fine iron ore which has not been captured by the second cyclone is collected by the third cyclone 60 to be circulated through the third circulation pipe 61 (connected to the first circulation pipe) to the second pre-reduction furnace. The iron ores which have been pre-reduced in the second and third pre-reduction furnaces for the second time are discharged respectively through a third outlet 23 and a fourth outlet 33.
In FIG. 1, reference numerals 12, 22 and 32 indicate gas distributors, and 11, 21 and 31 indicate gas inlets.
However, in the conventional fluidized bed type pre-reduction furnace of FIG. 1, the fine iron ore which has not been captured by the first cyclone 40 is discharged through the gas discharge conduit 42, with the result that the elutriation loss of the iron ore is very large.
Particularly, during the pre-reduction of the iron ore, the powderizing phenomenon occurs mostly at the early stage of the reduction. Therefore, a large amount of fine iron ore is scattered after it is powderized during the first pre-reduction by the first pre-reduction furnace 10 and after the mechanical powderizing caused by the fluidizing. Thus the first cyclone is overloaded, and therefore, the separation of the iron ore from the off-gas is inhibited, with the result that a large amount of fine iron ore is discharged together with the off-gas, thereby increasing the iron ore loss.